I have been using Slo Mo for the last few jobs and the stuff is AWESOME! It's crazy concentrated so it only takes a few ounces to do an entire roof. It also seems to clean extremely well and rinses easily. Try it you'll like it! I will definitely buy it again and nothing else.
They will call you and say that people in your area are looking for roof cleaners and that is probably true. What they don't tell you is that they are only IMPLYING these people are looking on Homeadvisor. They make it all sound really good, too. I guess it gets easy to make it sound good when it's all you do all day if you remember which lines people tend to fall for and use them. Leads, SEO, first page of Google, blah, blah, blah.
1" air pump is a good option. However, if you buy a used aodd pump for any roof cleaning operation be prepared to be disappointed. Chances are very good the pump will be 10 years + old and parts may or may not be even be available. Be prepared to have the used pump crap out in a year or less and then having to try to learn how to repair it IF you can find the parts and it's NOT easy to repair the air end if you've never done it. Time is money and spending an entire day or more working a pump doesn't cut it. Save yourself a lot of headaches and just buy new. It may cost you more up front but having a crapped out used pump AND a brand new one isn't cheap either!
The Eaton is a fine air compressor I am sure, but I know big HF ac is a beast because I have one and it will give you all the air you need. If you can afford the size and weight, the bigger air tank and smaller price tag for the HF make it a good choice, IMO.
No offense, but the "expensive, shiny" trap didn't stop with the system you greatly over paid for. I just looked at the surfactant you are using. $6.50 of that for every 50 gallon batch? That is a little steep, to say the least!
It will work for sure on siding and not at all on roofs. You may have to let it dwell for a few minutes before rinsing and may have to reapply a few times if really bad, but in most cases one application will be enough. I greatly prefer using my dedicated pump to clean siding over downstreaming with a pw but both have their advantages. The pw only requires the one hose which is nice, but I can apply the mix quicker with my dedicated pump, shoot much higher, use a stronger mix and rinse in a fraction of the time.
There is no one size fits all but it doesn't take much imagination in my opinion to see how only needing to carry full strength SH and mixing as you go at whatever strength you want is a real advantage for some especially those of us who can't carry 1000's of pounds of mix around and that do lots of house washes AND roof cleanings at the same locations. That being said, starting from completely empty I can make a 55 gallon batch in less than 5 minutes and can cut down a roof mix to a house mix or bump up a house mix to a roof mix in much less than that so its not a huge deal either way for me and regardless of the system you still have to go to the rig to change it. Now if the Proportioner were on a remote control.....now you're talking!
I don't usually bring water either. That's why I said the first thing I do is hook up to the ho water supply while I get everything else ready. You can actually use a drum that you set outside of the trailer when you get to job site if you have a long enough suction hose to reach it. That way you keep the weight out of the trailer entirely.
You only need to vent your tanks if they are in an enclosed system. Otherwise it's vented when you open the lid. Keep your battery in the box preferably in a location it won't be constantly doused with roof mix and don't worry about it. It's perfectly fine. The fumes aren't a concern with it either. Keep spills in the trailer to a minimum and it will last a long time. Drips here and there are not going to cause big problems. Avoid letting your mix overflow when making or especially your full strength when pumping into your tank. Keep things out of the trailer like your saw that don't need to be in there. Will it last forever? No, but it will make you a bunch of money before it dies.
I use a 55 gallon drum for a buffer tank with a Hudson float valve installed. First thing I do at a job is hook it up to the HO water supply. It makes making mix much faster than before as my 1" pump drawing water from the buffer tank is MUCH faster than waiting on a hose to fill my tank. Even bad water pressure can fill the buffer tank while I get everything else ready and I can make a 55 gallon batch in less than 5 minutes. If I need another batch the buffer is full and waiting. I would assume even with an electric pump you make mix much faster using a buffer than without.